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) STATES DEPARTMENT OF AGRICULTURE 



BULLETIN No. 282 



Contribution from the Bureau of Plant Industry 
WM. A. TAYLOR, Chief 




Washington, D. C. 



PROFESSIONAL PAPER 



August 11, 1915 



A STUDY OF THE SOFT RESINS IN SULPHURED AND UNSUL- 
PHURED HOPS IN COLD AND IN OPEN STORAGE. 

By G. A. Russell, 
«• 

Expert, Drug-Plant and Poisonous-Plant Investigations. 



CONTENTS. 



Page. 
Introduction 1 

Preparation of the hops studied 2 

Changes in physical appearance 3 

Moisture content and changes in the propor- 
tion of soft and hard resins 4 



Changes in the composition of the soft resins . . 10 

Chemical values of the soft resins 15 

Summary 18 



INTRODUCTION. 

During the past decade the soft resins of hops have been the sub- 
ject of numerous investigations wliich have dealt almost exclu- 
sively with the percentage of yield and the methods of extraction. 
With the exception of the work of Fischer/ no statements have been 
found in the literature to show that recognized chemical methods 
have been used to determine the changes which occur in the soft 
resins of hops subsequent to harvesting. The effect of refrigeration 
on the physical condition and on certain chemical constituents of sul- 
phured and unsulphured hops has been studied by Stockberger and 
Rabak/ who gave special consideration to the changes which occur 
in the volatile oil. Aside from the changes noted by these authors, 
extensive modifications also occur in the soft resins of hops, the 
character of which may be determined through the use of reliable 
analytical methods. 

1 Fischer, Alfred. Analysis of hops as a basis for their valuation. In Pure Products, v. S, no. 10, 
p. 5.36-538. 1912. 

2 Stockberger, W. W., and Rabak, Frank. Some effects of refrigeration on sulphured and unsulphured 
hops. U. S. Dept. Agr., Bur. Plant Indus. Bui. 271, 21 p. 1912. 

Note.— This bulletin presents the results obtained from experiments conducted to determine the extent 
and character of the changes in the soft resins in hops under varying conditions of curing and storage. The 
soft resins, or so-called bitter aci4s, are a principal factor in determining the commercial value of hops. 
98657°— Bull. 282—15 1 



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2 BULLETIN 282, V. S. DEPARTMENT OF AGEICULTURE. 

In order to obtain additional data regarding the effect of various 
storage conditions upon the soft resins of sulphured and unsulphured 
hops, a quantity of material was prepared and held under observa- 
tion for several years. The data secured indicate that there is a 
marked chemical rearrangement or balancing of at least a part of the 
components of these resins during the first year after the hops are 
harvested. This rearrangement is most marked in hops kept in cold 
storage, and of these it is most evident in the unsidphured hops. 

It is generally conceded that the commercial value of hops is almost 
entirely contingent upon two considerations, namely, the character 
of the aroma and the nature and quantity of the soft resins. At the 
last International Hop and Barley Exhibit, held in Chicago in 1911, 
the score card gave an equal rating to aroma and to the soft resins, or, 
as they are sometimes termed, the hop bitter acids. 

Although sulphuring and cold storage are efficient factors in retard- 
ing the diminution of the quantity of soft resins in hops, they do not 
prevent chemical changes from taking place therein. Nevertheless, 
the data obtained by the study of these changes indicate that they 
are influenced to a considerable degree by both sulphuring and cold 
storage. The experiments detailed in the following pages were made 
with a view to determining the extent and character of these changes. 

PREPARATION OF THE HOPS STUDIED. 

Since soil and climate, as well as other factors, are undoubtedly 
responsible for the varying quantity of soft resins found in hops of 
different geographical origin, all the samples of hops used in this 
investigation were secured from a common source, in order to elimi- 
nate variation so far as possible. Accordingly, two lots of hops 
harvested from the same field at Perkins, Cal., in September, 1911, 
were dried in ordinary hop kilns, one portion without being sulphured, 
the other receiving the customary sulphuring in the early stages of 
drying. Duplicate samples of each lot were then placed in hermeti- 
cally sealed tin cans and shipped to Washington, D. C. About the 
1st of December one sample each of the sulphured and unsulphured 
hops was subjected to analysis, and the remaining samples, each 
weighing 2 kilograms, were then removed from the tins, compressed 
to about the same degree as the hops in a commercial bale, and com- 
pletely inclosed in a cover of ordinary hop sacking. Three each of 
those sulphured and unsulphured samples were then placed in cold 
storage in the hop storeroom of a local brewery, and a similar set of 
samples was placed in the attic of a frame building at the Arlington 
Experiment Farm, Virginia. On December 1 of each of the three f ol- 
lov/ing years one sample each of the sulphured and the unsulphured 
hops was withdrawn from cold and open storage, respectively, and 
subjected to analysis. 

a «F a. 

AUa 2.(1 ''9^5 



r" SOFT RESINS IN SULPHURED AND UNSULPHURED HOPS. 

CHANGES IN PHYSICAL APPEARANCE. 



> 



On receipt of the various samples of hops from Perkins, Cal., in 
1911, they were examined and the following notes taken respecting 
their physical characteristics: 

Sulphured hops in the original lot. — Fine fresh hop flavor; oily feeling; h:pulin 
sticky; aroma excellent; color bright, characteristic of new fresh hops; color of 
lupiJin bright. 

Unsulphured hops in the original lot. — Fine fresh hop flavor; oily feeling; Ir.pulin 
sticky; aroma excellent; color bright, characteristic of new fresli hops, thorgh some- 
what greener in appearance than the corresponding snlphitred sample; color of Ir.pr.lin 
bright. 

(3n December 1 of the three following years, two samples each 
from cold and from open storage were examined and the following 
notes were taken on their physical characteristics: 

Sulphured hops in cold storage one year. — Fresh hop flavor; oily feeling; lupnlin 
sticky; aroma good; color darker than the original sample, not so briglit and charac- 
teristic; color of lupulin bright. 

Unsulphured hops in cold storage one year. — Fresh hop flavor; oily feeling; lupulin 
sticky; aroma good; color much darker than the original sample, not so bright and 
characteristic; color of lupulin bright. 

Sulphured hops in open storage one year. — Strawlike flavor; oily feeling; lupulin 
less sticky; aroma disagreeable; color dull, bright color ha\ing disappeared; color of 
lupulin dull. 

Unsulphured hops in open storage one year. — Strawliko flavor; oily feeling less notice- 
able; lupulin less sticky; aroma disagreeable; color A^ery dull; color of lupulin dull. 

Sulphured hops in cold storage two years. — Decided strawlike flavor; oily feeling very 
slight; lupulin slightly sticky; aroma slightly hoplike; color dark yellow, brightness 
having disappeared; color of lupulin dull. 

Unsulphured hops in cold storage two years. — Most decided strawlike odor, somewhat 
musty; oily feeling practically gone; lupulin not sticky; aroma like musty straw; color 
dark brownish yellow; color of lupulin very dull. 

Sulphured hops in open storage two years. — Decided strawlike flavor; oily feeling 
practically gone; lupulin slightly sticky; aroma that of musty straw; color dark brown- 
ish yellow; color of lupulin very dull. 

Unsulphured hops in open storage two years. — Very decided musty flavor; oily feeliu"- 
gone; lupulin very slightly sticky; aroma that of musty straw; color dark brov.'nish 
yellow; color of lupulin very dark and dull. 

Sulphured hops in cold storage three years: — Most decided strawlike flavor, somewhat 
musty; oily feeling gone; lupulin very slightly sticky; aroma that of old musty straw; 
color dark brownish yellow; color of lupulin A^ery dark and dull: hop cones falling 
apart. 

Unsulphured hops in cold storage three years. — Very decided musty, strawlike fluAor; 
oily feeling entirely gone ; lupulin not sticky ; aroma that of old musty straw ; color Aery 
dark, dirty brownish yellow; color of lupulin very dark and dull; hop cones falling 
apart. 

Sulphured hops in open storage three years. — Very decided musty, strawlike flavor; 
oily feeling entirely gone; lupulin not sticky; aroma that of old musty straAV; color dark 
broAvnish yelloAv; color of lupulin very dark and dull; hop cones fallen ajjart. 

Unsulphured hops in open storage three years. — Most decided musty, straAvUke flavor; 
oily feeling entirely gone; lupulin not sticky; aroma that of old musty straw; color A'ery 
dark brownish yellow; color of lupulin A-ery dark and dull; ho]i cones fallen apart. 



4 BULLETIN 282, U. S. DEPARTMENT OF AGEICULTTJRE. 

As far as physical valuation indicates, the sulphured hops in cold 
storage deteriorated at a slower rate than the unsulphured hops, and 
the same is true for the samples placed in open storage. At the end 
of one year of storage very little phj^sical difference could be noticed 
in the cold-storage hops other than that the color had darkened in 
both the sulphured and unsulphured samples, more especially in the 
latter. The samples in open storage at the end of one year had each 
developed a strawlike odor and had become dull in color. The 
lupulin of both the sulphured and unsulphured hops had begun to 
lose its brightness and its sticky feeling. 

At the end of the second year of storage a most decided change had 
taken place in all the samples. The sulphured hops in cold storage 
had developed a strawlike flavor and a dry feeling and the bright 
color had disappeared. The unsulphured samples had developed a 
musty odor and an extremely dry feeling, and the characteristic 
greenish yellow color had disappeared. The unsulphured hops had 
deteriorated more rapidly than the corresponding sulphured hops. 
So far as the physical valuation indicated, the hops in open storage 
had deteriorated to a much greater degree than the hops in cold 
storage. The unsulphured samples in open storage had become very 
musty in odor and very dark in color, in addition to losing their 
crisp and sticky feeling. 

At the close of three years of storage the samples had lost all traces 
of hop flavor and had developed a musty, strawlike odor. A slight 
stickiness could still be detected in the sulphured hops in cold storage. 
The hop cones in the cold-storage samples had fallen apart to some 
extent, whereas those in the open storage samples had completely 
fallen apart. The lupulin in all the samples was much discolored. 

MOISTURE CONTENT AND CHANGES IN THE PROPORTION OF SOFT 

AND HARD RESINS. 

At the time the hops were received m Washington a sample each of 
the sulphured and unsulphured hops was analyzed and the results 
thus obtained were used as the basis for comparing the analyses which 
were made of the various samples during each year of storage. 

MOISTURE CONTENT. 

For the determination of the moisture content 12 grams of hops 
were taken from each of the samples under investigation, dried over 
sulphuric acid until of constant weight, and the loss in weight 
returned as moisture. The moisture content of the original hops and 
of the hops in both cold and open storage for the several years is 
given in Table I. 



SOFT RESINS IN SULPHURED AND UNSULPHURED HOPS. 



Table I. — Moisture in the original samples of sulphured and unsulphured hops and in 
samples hept in cold and in open storage. 



Treatment at the kiln. 


Original 

sample, 

1011. 


Cold storaKC 


Open storage. 


1012 


1913 


1914 


1912 


loi:! 1914 


Sulphured 

Unsulphure.d 


Per cent. 
6. IS 
5.23 


Per cent. 
11.04 
10. SO 


Per cent. 
11.04 
10.79 


Per cent. 
9.83 
10.90 


Per cent. 
5.81 
6.14 


Per cent. 
6.37 
5.90 


Per cent. 
6.40 
5.50 



From Table I it is evident that the moisture content of the hops 
kept in cold storage was greater than of those in open storage. In 
the samples kept hi cold storage the moisture content was very 
uniform for the three years in both the sulphured and the unsul- 
phured hops, indicating that the cold-storage room was kept at a 
uniform temperature throughout this pericnl. In the open-storage 
samples a slight fluctuation in the moisture content was evident, due 
apparently to differences m the atmospheric conditions at the time 
the samples were removed for analysis. Since moisture is an imjior- 
tant adjunct to a great many chemical changes, it is probable that 
the greater quantity found in the samples kept in cold storage had a 
direct bearing on the chemical changes that took place in the soft 
resins. 

SOFT RESINS. 

In determining the quantity of soft resins hi the hop samples, a 
departure was made from the method usually employed. A kilo- 
gram of hops was extracted by maceration and percolation with 
petroleum ether (B. P. 35° C. to 70° C). Two macerations were 
necessary to complete the extraction. The mixed percolates were 
then heated on a water bath at 70° C. and the major portion of the 
petroleum ether recovered. The remainder of the petroleum ether 
was allowed to evaporate spontaneously and the weight of the residue 
returned as soft reshis. The residues each contained a small fraction 
of approximately 0.4 per cent of wax, which for purposes of com- 
parison may be disregarded. The percentage of soft resins in the 
original sulphured and unsulphured samples and in the corresponding 
samples in cold and in open storage is shown in Table II. 



Table II. 



-Soft 7-esins in the original samples of sulphured and unsulphured hops and 
in samples kept in cold and in open storage. 



Treatment at the kiln. 


Original 

sample, 

1911. 


Cold storage. | Open stora;-:c. 


1912 


1913 


1914 


1912 


19i:i 


1914 


Sulphured 

Unsulphured 


Per cent. 
12.32 
11.17 


Per cent. 
11.91 
9.72 


Per cent. 
11.46 

8.66 


Per cent. Per cent. 
4.98 11.32 
3.81 S.73 


Per cent. 
9.03 
7.43 


Per cent. 
3.20 
2.32 



BULLETIN 282, U. S. DEPAETMENT OF AGRICULTURE. 



Regarding, first, the sulphured hops, the data in Table II show 
that the percentage of soft resins decreased somewhat during the 
first and second years of storage and very rapidly during the third 
year. The decrease was less, however, in the cold-storage samples 
than in those kept in open storage. The unsulphurcd hops show a 
marked decrease from year to year, the decrease being most pro- 
nounced in the third year of storage. The unsulphured samples in 
open storage show a greater loss than the corresponding samples 

kept in cold storage. 
Durmg the first year 
of open storage the 
soft-resin content in 
the sulphured hops 
decreased less rap- 
idly than in the un- 
sulphured hops, but 
more rapidly in the 
following two years. 
It will be observed 
from figure 1 that 
the quantity of soft 
resins present in the 
sulphured hops in 
both cold and open 
storage decreased 
during each year and 
that the decrease was 
especially marked 
during the third year 
of storage. Figure 1 
also shows that the unsulphured hops in cold storage decreased in 
soft-resin content more rapidly than the sulphured hops and that 
this decrease was rapid during the first year, less pronounced during 
the second year, and at the end of the third year gradually ap- 
proached the same point of value as in the sulphured hops in cold 
storage. The soft-resin content of the misulphured hops in open 
storage decreased at about the same rate as that of the sulphured 
hops in open storage. 

The percentage of decrease in soft resins during the three years, 
as compared with the original samples, is given in Table III. 




y^C/iffS //V STORAGE 



Fig. 1.— Curves of the percentage of soft resins in sulphured and un- 
sulphured hops in cold and in open storage. 



SOFT RESINS IN SULPHURED AND UNSULPHURED HOPS. 7 

Table III. — Decrease in the soft resins of sulphured and unsulphured hops in cold and 
in open storage compared with the soft-resin content of the original samples. 





Original 

sample, 

1911. 


Cold storage. 


Open storage. 




1912 


1913 


1914 


1912 


1913 


1914 


Sulphured 

Unsulphured . . 


Per cent. 
100 
100 


Per cent. 
3.32 
12.98 


Per cent. 
6.98 
22.47 


Per cent. 
59. 57 
65.89 


Per cent. 

8.11 

21.84 


Per cent. 
26.71 
33. 48 


Per cent. 
74.02 
79.23 





From Table III, in which the soft-resin content in the origintil 
samples is considered as 100 per cent, it is evident that the decrease 
in the sulphured hops during the first two years in cold storage was 
not great, but it was rapid during the third year. In open storage 
the decrease was very pronounced during each year. The unsul- 
phured hops in cold storage show a marked decrease, which was 
gi-eatest in the third year, and in open storage the decrease was even 
more pronounced year by year. 

HARD RESINS. 

The hard resins in the various samples of hops used in this study 
were also determined. A portion of tlie hops after being extracted 
with petroleum ether was again extracted with ether, the ether 
recovered, and the weight of the residue returned as hard resin. 
By this method an extra calculation is necessarj^, but in using large 
quantities of hops the time consumed is more than compensated for 
in the accuracy obtained. 

The hard-resin content of the various samples is shown in Table IV. 

Table IV. — Hard resins in the original samples of sulphured and unsulphured hops 
and in samples kept in cold and in open storage. 



Treatment at the kiln. 


Original 

sample, 

1911. 


Cold storage. 


Open storage. 


1912 


1913 


1914 


1912 


1913 


1914 




Per cent. 
5.26 
6.43 


Per cent. 
6. .53 
8.35 


Per cent. 
8.97 
10. 08 


Per cent. 
9.90 
10.05 


Per cent. 
8.32 
9.53 


Per cent. 
9.09 
10. 45 


Per cent. 
10. 10 




10.46 







The figures in Table IV give an index of the change in the quantity 
of hard resins that took place in the various hop samples. The 
greatest change occurred in the unsulphured hops in open storage 
and the least change in the unsulphured hops during the first two 
years in cold storage. The difference in the content of hard resins 
of both sulphured and unsulphured hops in cold and in open storage, 
respectively, became materially less in the third year of storage and 
probably indicates that the changes which took place in the hops 



8 BULLETIN 282, U. S. DEPARTMENT OF AGEICULTURE. 

tended to reach a state of equilibriiun irrespective of the treatment 
of the sample. 

Figure 2 gives a graphic representation of the increase in the hard- 
resin content of sulphured and unsulphured hops in cold and in open 
storage. 

During the first year the increase in the hard-resin content in 
the sulphured hops was greater in open storage than in cold storage. 
-Vt the end of the second year the sulphured hops in both cold and 

open storage con- 
tained about the 
same percentage of 
hard resms. The 
unsulphured hops 
followed the same 
lines, but did not 
present quite so 
marked a difference 
durmg the first year 
of storage. At the 
end of the third 
year the hard-resin 
content m all the 
samples had become 
uniform and a state 
was reached where 
the increase, if any, 
was very slow. 

Table V gives the percentage of mcrease in the hard-resin content 
of the various samples as compared with the original, the hard-resin 
content of the latter ])eing considered as 100 per cent. 

Table V. — Increase in the hard resins of sulphured and unsulphured hops in cold and 
in open storage, compared with the hard-resin content of the original samples. 




y£^/?S //y STOPAGE 
-Curves of the percentage of hard resins in sulphured and un- 
sulphured hops in cold and in open storage. 



Treatment at tlie kiln. 



Original 

sample, 

1911. 



Cold storage. 



1912 



Open storage. 



Sulphured 

l^nsulphured. 



Per cent. 
100 
100 



Per cent. 
24.14 
29.85 



Per cent. 
70.53 
52.75 



Per cent. 
88.21 
56.29 



Per cent. 
58. 17 
48. 21 



Per cent. 
72.81 
62.51 



Per cent. 
92.01 
62.67 



The sulphured hops appeared to react less readily to changes that 
brmg about an increase in the hard resins. From this it is uif erred 
that sidphm-mg is a factor that retards the changing of soft resms 
to hard resins. This is shown most emphatically in Table V by the 
fact that the percentage of increase in the misulphured hops was much 
less in both cold and open storage than in the corresponding sulphured 



SOFT EESINS IN SULPHURED AND UNSULPHUKED HOPS. 



9 



hops. A further study of Tabh^ V mdicates that a combination of 
sulphuring and cokl storage was most effective in retardmg the 
changes that produce hard resins. 



TOTAL RESINS. 



The total resin content of the various hop samples, found by adding 
the soft resins and tlie hard resins together, is shown in Table Yl. 

Table VI. — Total resins in the original samples of sulphured and unsulpJiured hops 
and in samples kept in cold and in open storage. 



Treatment at the kiln. 



Sulphured 

Unsulphured. 



Original 
sample, 

ion. 



P(r cent. 
17. 58 
17.60 



Told storage. 



Per cent. 
18. -14 
18. 07 



Per cent. 
20. 43 
18. 74 



Per cent. 
14. 88 
13. 86 



cipen storage. 



Per cent. 
19.64 
18.26 



Per cent. 
IS. 12 
17.88 



Per cent. 
13.30 

12. 78 



From the figures in Table VI it appears that some tliscrepancies 
exist, since the total resins in some years ran higher than those of 
the original sample. Experiments in this laboratory have shown that 
two samples are rarely ever the same in total yield of resms ; hence, no 
weight need be attached to the apparent discrepancies. 

The sudden decrease in the total resins in all the samples in the 
year 1914 is of special interest. Up to this point the hops in storage 
had retained approximately their original content of soft resms. A 
marked diminution now occurred in the content of soft resms, which 
is not compensated by a corresponding increase in the content of 
hard resins. It appears from the data at hand that a portion of 
the soft resins had been transformed into a compound or compounds 
insoluble in ether or in petroleum ether, since the marked loss in 
percentage of soft resms does not appear in the ether extract. The 
extent of the change was greatest in the unsulphured hops in open 
storage and least in the sulphured hops in cold storage, but m all 
samples, irrespective of treatment either at the kiln or during storage, 
the decrease was rapid. Table IV shows that at the end of the second 
year of storage a point was reached by all the samples beyond which 
the hard resins did not materially increase. Nevertheless, at this 
point the soft resins began to decrease most rapidly. Although pre- 
vious investigators have stated that the soft resins change entirely 
to hard resins, it is probable that only a small portion of the soft 
resins undergoes such a change, and the remamder is changed into a 
compound or compounds insoluble in the solvents used m extraction 
and for that reason is lost sight of in the analysis. 
98657°— Bull. 282—15 2 



10 



BULLETIN 282^ U. S. DEPARTMENT OF AGRICULTURE. 



Table VII. — Soft resins in the original samples of sulphured and unsulphured hops 
and in samples kept in cold and in open storage, calculated with reference to the totnl 
resins. 



Treatment at the kiln. 


Original 

sample, 

1911. 


Cold storage. 


Open storage. 


1912 


1913 


19H 


1912 


1913 


1914 


Sulphured 


Per cent. 
70.13 
63.46 


Per cent. 
64.59 
53. 79 


Per cent. 
56.08 
46.21 


Per cent. 
33.47 

27.49 


Per cent. 
57.63 

47. 80 


Per cent. 
49.83 
41.55 


Per cent. 
24.06 




18.15 







The data in Table VII show that the sulphured cold-storage hops 
retained a greater percentage of soft resins each year than did any of 
the other samples. The unsulphured hops in cold storage and the 
sidphured hops in open storage contained year by year practically the 
same percentage of soft resins, as calculated with reference to the 
total resins. The greatest decrease is noted in the soft resins from 
the unsulphured hops in open storage. 

CHANGES IN THE COMPOSITION OF THE SOFT RESINS. 

That chemical changes take place in the soft resins of hops is a 
foregone conclusion. In order to study these changes, methods in 
general use in chemistry, with some modifications, were applied to 
the soft resins with satisfactory results. The physical properties of 
color and odor presented in Table YIII were observed from year to 
year. 

Table VIII. — Physical properties of the soft resins in the original samples of sulphured 
and unsulphured hops and in samples kept in cold and in open storage. 



Treatment at the kiln. 


Original sample, 
1911. 


Cold storage. 


1912 


1913 


1914 


Color: 

Sulphured 


Greenish brown. 
Dark brown 

Aromatic, pleas- 
ant. 
do 


Dark brown 

Ve r y dark 
brown. 

Aromatic, pleas- 
ant. 

Aromatic, pun- 
gent. 


Greenish brown, 
do 




Unsulphured 


Do. 


Odor: 


Aromatic, pleas- 
ant. 

Agreeable, hop- 
like. 






pleasant. 
Do. 









Treatment at the kiln. 


Original sample, 
1911. 


Open storage. 


1912 


1913 


1914 


Color: 


Greenish brown. 


Dark brown 

do 


Greenish l)rown. 
do 






Do. 


Odor: 

Sulphured 


Aromatic, pleas- 
ant. 

do . 


Aromatic, pleas- 
ant. 

Aromatic, pun- 
gent. 


Aromatic, pleas- 
ant. 

Aromatic, pun- 
gent. 


Disagreeable, 
somewhat aro- 
matic. 
Do. 


Unsulphured 









SOFT EESINS IN SULPHURED AND UNSULPHUEED HOPS. 



11 



All the samples had an extremely bitter taste, manifested strongly 
at the base of the tongue when a minute particle of the soft resin was 
held in the mouth for a few seconds. 

Tlie color, odor, and taste, which appeal solely to the senses, are of 
relatively small importance in this investigation. As shown in Table 
VIII, the color of the soft resins in all cases became darker with the 
age of the sample examined; the odor became very disagreeable with 
the decrease of the soft resins and the taste at aU times remained very 
bitter. 

The soft resins are fluid in nature, and during the first two years of 
storage all were of the same consistency. Those extracted in 1914 
were more solid and had the consistency of a thick sirup. Owing to 
their nature, the specific gravity of these resins could not be deter- 
mined with accuracy. 

ACro AND ESTER VALUES. 

The determination of the free acidity or acid value of the soft 
resins was carried out as foUows: A small quantity of w^eighed soft 
resin was taken up in 2 c. c. of standardized alcoholic potassium 
hydroxid and the excess potassium hydroxid titrated back with N/10 
hydrochloric acid. The acid value represents the number of milli- 
grams of potassium hydroxid necessary to completely neutralize the 
free acids in 1 gram of the soft resins. 

In determining the ester value of the soft resins a weighed portion 
was taken up in standardized alcoholic potassium hydroxid and 
allowed to stand 24 hours in the cold. Complete saponification took 
place in that length of time. The excess alkali was titrated back 
with N/10 hydrocliloric acid and the saponification value calculated. 
This value, minus the acid value, gives the ester value of the soft 
resins and represents the number of milligrams of potassium hydroxid 
necessary to completely saponify aU the combined acids in 1 gram 
of the soft resins. The changes observed in the acid and ester values 
are shown in Table IX. 

Table IX. — Acid and ester values of the soft resins in the original samples of sulphured 
and unsulphured hops and in samples kept in cold and in open storage. 



Treatment at the kiln. 


Orisinal 

sample, 

1911. 


Cold .storage. 


Open storage. 


1912 


19i:3 


1914 


1912 


1913 


191-1 


Acid value: 

Sulphured 


71.80 
60.87 

97.7 
121.78 


97.00 
67.00 

169. 5 
71.. 5 


87. .50 
76.50 

191.1 
S7.0 


80.7 
76.2 

226.3 

207.8 


72.5 
52.0 

122. 5 
123.5 


61.50 
70.00 

202.5 
158.0 


47.0 

77.6 


Ester value: 

Sulphured 


271.0 


Unsulphured 


158. 4 



12 



BULLETIN 282, U. S. DEPAETMENT OF AGRICULTURE. 



A graphic representation of tlie acid values is given in figure 3. 
From this figure it will be seen that after the first year of storage the 
acid value of the soft resins diminished in the sulphured hops and 
gradually increased in the unsulphured hops. The rise in acid value 
of the soft resins of the sulphured hops during the first year in cold 
storage was probably due to the rearrangement that was taking place 
in these resins; although esters were formed during this period the 
esterification did not proceed as rapidly as in the following years, 
with a consequent rise in free-acid value. During the first year of 
open storage the acid value of the soft resins of the sulphured hops 
remained about the same and then gradually decreased at a rate 
proportionate to that of the sulphured hops in cold storage. The 
formation of esters was slow during the first year of storage and rapid 

during the next tv\'0 
years, reaching a 
slightly higher value 
at the end of the 
third year than in the 
corresponding sam- 
ple in cold storage. 

The unsulphm^ed 
hops in cold storage 
yielded soft resins 
whose acid value 
constantly increased 
throughout the pe- 
riod of storage. The 
ester value for these 
soft resms decreased 
during the first year, then gradually increased durmg the second 
year, and very rapidly during the third year of storage. In open 
storage the acid value in the unsulphured hops was slightly less at the 
end of the fii'st year than in the corresponding original sample. The 
ester value (fig. 4) remained almost constant, indicating that there 
was little change in these values during the first year of storage. 
From this point the acid values from the rmsulphured hops increased 
gradually, until at the end of the third year of storage about the 
same degree of acidity was reached. 

The increase in acidity was, however, most marked in the unsul- 
phured hops in open storage. The ester values for the soft resins of 
the unsulphured hops increased after the first year of storage and 
was most rapid in the cold-storage samples. 

The acid value of the soft resins from sulphured hops in both cold 
and open storage gradually diminished at approxhiiately the same 
rate after one year of storage. The corresponding ester values in- 




FiG. 3.- 



y£^/?s //v sro/fyis£ 



•Acid-value curves of the soft resins in sulpliured anu unsul- 
phured hops in cold and in open storage. 



SOFT RESINS IN SULPHURED AND UNSULPHURED HOPS. 



13 



creased in approximately the same proportion as the acid values 
diminished . This 
decrease in the acid ^'*'"" 
value a n d increase 
in ester value would 
indicate that ester- 
ification took place 
faster than free acids 
were formed, the 
original quantit}' of 
free acids being prac- 
tically used up. In 
other words, the sul- 
l^huring of hops ap- 
pears to hasten the 
formation of esters 
ui the soft resins but 
retards the forma- 
tion of free acids. 

The acid value of 
the soft resins from 
the sulphured hops 
m both cold and open 
storage gradual!}' in- 
creased during the period of storage, and the correspondhig ester value 

likewise gradually 
increased, indicatmg 
that in the unsul- 
phured hops the for- 
mation of free acids 
and of the corre- 
sponding esters goes 
on with regularity. 

SAPONIFICATION VALUE. 




y£:^/?s //v sro/fy^GS 



Tig. 4. — Ester-value curves of the soft resins in sulphured and imsul- 
phured hops in cold and in open storage. 



K /SO 



-^ 



.1^ 



<^^ 



.yU>JiS^ 



</r££^ 



"^^ 



rO^AS f- 



t°-!^' off' 




^^^^ 



3 
W^'- 



o^:- 






The saponification 
value, shown in Ta- 
ble X and indicated 
graphically in figure 
5, was in this study 
determined before 
the ester value, al- 
though it is usually 
obtained by adding 
the acid and ester values of the product under investigation. From 



-Saponifieation-value curves of the soft resins in sulphured and 
unsulphured hops in cold and in open storage. 



14 



BULLETIN 282, U. S. DEPARTMENT OF AGRICULTURE. 



a study of the ester and acid values, a gradual increase in the saponin 
fication value would be expected. This mcrease was most marked after 
the first year of storage, and all the samples gradually approached a 
uniform value. The saponification value of the soft resins from the 
sulphured hops was slightly higher than the same value in the un- 
sulphured hops. The increase m the saponification value was most 
uniform in the hops held in open storage and was most rapid during 
the tliird year in the unsulphured hops in cold storage. 

Table X. — Saponification value of the soft resins in the original samples of sulphured 
and unsulphured hops and in samples kept in cold and in open storage. 



Treatment at the kiln. 


Original 

sample, 

1911. 


Cold storage. 


Open storage. 


1912 


1913 


1914 


1912 


1913 


1914 




169.5 
1S2. 65 


266.5 
138.5 


278.5 
163.5 


317 
284 


195 
175.5 


264 

228.5 


324 




236 







lODIN VALUE. 

In determining the iodin-absorption value of the soft resins, the 
method employed was that commonly used in determining this value 
in fats. The results obtained are shown in Table XI. 

Table XI. — lodin value of the soft resins in the original samples of sulphured and 
xinsulphured hops and in samples kept in cold and in open storage. 



Treatment at the kiln. 


Original 

sample, 

1911. 


Cold storage. 


Open storage. 


1912 


1913 


1914 


1912 


1913 


1914 




95 

100 


76 

72 


144 
140 


156 
141 


123 

89 


132 
143 


156 




15* 







The iodin values, as shown in Table XI and in figure 6, became 
less divergent in the third year of storage. In the soft resins from 
the sulphured hops in open storage the iodin value gradually increased 
for each year of storage. In all the other samples it diminished 
durmg the first year, rose rapidly during the second year, and in the 
third year was uniform with that from the sulphured hops in open 
storage. This indicates a diminution in the unsaturated compounds 
in the soft resins from the sulphured hops in cold storage and from 
the unsulphured hops in both cold and open storage and an increase 
in the unsaturated compounds in sulphured hops in open storage 
during the first year. It wiU be noted, however, that after the com- 
pletion of the marked readjustment that took place during the first 
year of storage, the iodin value of all the samples tended to become 
uniform, thus indicating that the unsaturated compounds were present 
in approximately the same proportion in all the soft resins of aU the hop 
samples at some point between the first and the second year of storage. 



SOFT EESINS IN SULPHUEED AND UNSULPHURED HOPS. 15 




y£r^fis //v sroA'^es 



Fig. 6.- 



lodiii-value curves of the soft resins in sulphured and un- 
sulphured hops in cold and in open storage. 



CHEMICAL VALUES OF THE SOFT RESINS. 

In order to make more apparent the correlation between the various 
chemical vakies found in the soft resins from year to year, these values 
have been brought 
together and are rep- 
resented graphically 
in figures 7, 8, 9, 
and 10. 

Figure 7 shows 
the various values 
as found in the sul- 
phured hops in cold 
storage. The acid 
value, which in- 
creased during the 
first year of storage, 
gradually decreased 
during the second 
and third years. The ester value, which increased very rapidly 
during the first year of storage, diminished somewhat during the 
next two years. Figure 7 shows also that although esterification 
took place rapidly during the first year of storage it could not keep 

pace with the forma- 
tion of free acids; 
thus the latter in- 
creased. During 
the remainder of the 
time the hops were 
in storage esterifica- 
tion continued, but 
the quantity of free 
acids formed was not 
so great, with the re- 
sult that there was 
a decrease in free 



Vj /so 



^y 



^ 



.^^ 






^^'^ 



u^^ 




Fig. 7. 



-Curves showing the correlation of chemical values of the 
soft resins in sulphured hops in cold storage. 



acidity. 

The saponification 
value gradually in- 
creased throughout 
the storage period. 
The iodin value at 
the end of the first year of storage was less than that of the original 
sample, indicatmg that the formation of unsaturated compounds in 
the soft resins had been retarded in the sample held in storage. The 
iodin value increased during the second year, indicating a greater 
production of unsaturated compounds in the soft resins. 



16 



BULLETIN 282^ U. S. DEPARTMENT OF AGRICULTUEE, 




Fig. 8.- 



yS^/PS /-^ STO/f^^GS 



-Curves showing the correlation of chemical vahies of the soft 
resins in sulphured hops in open storage. 



Figure 8 shows the various vahies as found in the sulphured hops 
in open storage. The acid vakie, which remained ahnost constant 

during the first year 
of storage, gradually 
diminished during 
the next two years. 
The ester value, 
which increased 
somewhat during the 
first year, increased 
rapidly during the 
second and third 
years, indicating that 
the esterification was 
slightly in advance of 
the formation of free 
acids at all periods of 
storage and became 
more pronounced at 
the close of the third 
year. The iodin 
value gradually increased, indicating the continuous formation of 
unsaturated compounds in the soft resms througliout the entire period 
of storage. The 
saponification value 
gradually increased 
throughout the 
period of storage. 

Figure 9 gives a 
graphic illustration 
of the various values 
as found in the \\\\- 
sulphured hops in 
cold storage. The 
acid value gradually 
increased throughout 
the period of stor- 
age. The ester value 
diminished during 
the first year of stor- 
age, increased some- 
what during the sec- 
ond year, and in the third year the increase was rapid. Figure 9 
shows also that esterification did not keep pace with the formation of 
free acids during the first year of storage. However, during the next 




y£At/?s ^^ sro/py^ss 



Fig. 9. — Curves showing the correlation of chemical values of the .soft 
resins in unsulphured hops in cold storage. 



SOFT EESINS IN SULPHURED AND UNSULPHUEED HOPS. 17 



/eo 
\ 



^f222£:eS"^^^2^ -^ 



^sr^^ t^y^^i/e 



two years it was more rapid, with a consequent increase in the ester 
vakie. 

The saponification value gradually increased after the first year of 
storage. The iodin value likewise increased after the first year, 
although during that year it diminished somewhat, but durmg the 
second year it increased rapidly, indicating thereby that the misatu- 
rated compounds formed in the soft resins also increased rapidly, and 
they remained fairly constant after this point was reached until the 
close of the third year. 

Figure 10 shows the various values as found in the unsulphured 
hops in open storage. The acid value diminished slightl}' during the 
first year and in- 
creased each year 
thereafter. The es- 
ter value increased 
slightly durmg the 
first year, quite rap- 
idly during the sec- 
ond year, and re- 
mained constant 
during the third 
year, esterification 
in this sample prac- 
tically keeping pace 
with the formation 
of free acids through- 
out the storage 
period. The saponi- 
fication value, which 
decreased slightly 
durmg the first year of storage, increased during the second and third 
years. The iodhi value decreased slightly during the first year, in- 
creased rapidly during the second year, and slightly durmg the third 
year, indicating thereby that the unsaturated compounds in the soft 
resms remamed fairly constant durmg the first year, increased rapidly 
during the second 3^ear, and were fairly constant during the third 
year of storage. 

The r(dations of these various values may be briefly summarized as 
follows : 

(1) A change took place in some of the components of the soft resins of the hops, 
indicative of a marked rearrangement in tliese compounds during the period that 
elapsed between picking the hops and the end of one year of storage. 

(2) This change was most pronounced in the hops in cold storage, irrespective of 
treatment at the dry kiln. However, on comparison, the unsulphured hops showed 
the greatest change. 



^se.<^i:£j^ic£r 



Fig. 10. — Curves showing the correlation of chemical values of the soft 
resins in unsulphured hops in open storage. 



18 BULLETIN 282, U. S. DEPARTMENT OF AGEICULTUEE. 

(3) This change was not so pronounced in the hops kept in open storage, irrespective 
of treatment at the dry kihi. On comparison, however, the iinsulphured hops showed 
the greatest change. 

(4) The most decided change occurred in the imsulphured hops in cold storage and 
the least marked change in the sulphured hops in open storage. 

(5) After the first year the degree of change in all the samples fluctuated with regu- 
larity from year to year. Taken in the aggi'cgate, the values as determined from year 
to year indicate most strongly that an extensive rearrangement took place in the soft 
resins of the hops from the time they were picked until some point was reached between 
the first and second year of storage. When this point was reached and the rearrange- 
ment had practically terminated, a gi'adual increase or decrease could be traced in all 
the values taken. 

SUMMARY. 

In 1911, material for a comparative study of the soft resins of 
sulphured and unsulphured hops in both cold and open storage was 
secured from a hop ranch at Perkins, Cal. Tlie green hops were 
divided into two lots, one of which was sulphured during the process 
of drying. The dry suli:)hured and unsulphured hops were again 
divided into lots, sealed in tin cans, and shipped to Washington, 
D. C. On arrival the cans were opened and an analysis ma(k^ of one 
lot each of the sidphurcd and unsulphured hops. The remainmg 
samples were baled in burlajj and three samples each of the sulphured 
and unsulphured hops were placed in both cold and open storage. 

At the end of the first, second, and third years of storage one 
sample each of the sulphured and unsulphured hops was withdrawn 
from both cold and open storage and an analysis made of each. The 
hops analyzed in 1911 are designated as "original hops," since they 
approximate more nearly the condition of the samples at the time of 
drying. 

A physical valuation was placed on the original samples and also 
on the hops as they were withdrawn from storage from time to time. 
From these valuations the conclusions are drawn that both sulphuring 
and cold storage retard changes in the physical characteristics of hops. 
A combination of the two factors is more effective in retarding these 
changes than either factor alone. 

Determmations were made of the moisture, the percentage of soft 
resins, hard resins, and total resins, of the color, odor, and taste of the 
soft resins, and of the acid, ester, saponification, and iodin values of 
the soft resms. 

The moisture content in the sulphm-ed and unsulphured hops held 
in cold storage increased during the first year and then remained 
practically constant in all the samples throughout the period of 
storage. The moisture content of the sulphured and unsulphured 
hops in open storage varied from year to year, according to existing 
weather conditions. 



SOFT KESIN6 IN SULPHURED AND UNSULPHURED HOPS. 19 

The percentage of soft resins in all the samples decreased with each 
year of storage, becoming very pronounced in the third year. The 
percentage of hard resins in all the samples increased with each year 
of storage, approaching a uniform figure at the close of the third year. 
Both sulphuring and cold storage retarded the decrease in the per- 
centage of soft resins and increased the percentage of hard resms. A 
combination of the two factors was more effective in retarding these 
changes than either factor alone. 

The percentage of total resins in all the samples varied from year to 
year, and in the third year it became materially less than that of the 
original sample. The low total is probably due to the formation of 
products insoluble in the solvents used. 

The color, odor, and taste of the soft resins are of very little value 
in determinmg quality and are not indicative of any changes that may 
have taken place therein. 

The acid value in general decreased in the sulphured hops in cold 
and m open storage and increased in the misulphured hops in cold 
and in open storage. Sulphuring apparently retards the formation 
of free acids, and a combination of sulphurmg and cold storage is 
most effective in retarding changes in free acidity. 

The ester value in general increased in all the samples of hops. 
Sulphm-mg apparently favors the formation of esters, and this factor 
in combination with open storage appears to be the least effective in 
retarding the formation of esters. Nonsulphurmg and open storage 
appear to be the most effective in retarding the formation of esters. 

The saponification value in general increased in all the samples of 
hops. The unsulphured hops showed the least change, and of these 
the ones held in open storage were the least affected. 

The iodin value in general increased in all the samples. It was 
most pronounced in the second year of storage and in the third year 
was miiform in all the samples. Sulpliuring in combination with 
open storage appears to cause a uniform rate of increase m the iodm 
value from year to year. The sulphured hops in open storage showed 
the least variation in changes in the chemical values of the soft resms. 

Durmg the period of storage, at least some of the components of 
the soft resins underwent rearrangement. This rearrangement was 
most marked during the first year, after which it decreased to such 
an extent that thereafter comparable values for the chemical constants 
were readily obtained. 

o 



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